What Happened to IPv5?

The version of Internet Protocol (IP) used on most computer networks today is four, typically called IPv4. The next version of IP expected to one day become the new worldwide standard is version six (IPv6). Some people who study computer networking are understandably curious to know what happened to the protocol version in-between, the hypothetical IPv5.

In short, IPv5 never became an official protocol. Many years ago, Internet Stream Protocol (ST) was considered IP version five by industry researchers, but ST was abandoned before ever becoming a standard or widely known as IPv5. Work on ST and IPv5 is not expected to ever restart.